Prior sighting devices have been provided for use in connection with aiming missile firing weapons for example, mortars. In the case of mortars to be fired in daylight, the mortar is usually established in an initial direction toward a target along a line termed an observation or datum direction, determined, for example, by means of two suitably spaced aiming posts located downrange of the mortar toward a selected target. The aiming posts are placed by dispatching personnel downrange from the mortar and locating the posts by audible or arm and hand signals given by personnel located at the weapon. The exposure to enemy fire, and resultant danger, to such personnel, particularly the downrange personnel is great. In order to aim the mortar, the aiming sight of the mortar is turned so that the plane of the axis of the aiming sight is in alignment with the aiming posts determining the observation direction and reference line. Usually two aiming posts are provided to establish a reference line, including a far aiming post usually being placed about 100 meters from the mortar and a nearer post placed about halfway between the far aiming post and the mortar itself. The reference line then provides a base reference for use in sighting the mortar to other nearby selected targets. When it is required to effect a fire switch through a given angle, that is to change the direction of fire for example through a certain angle toward the right, the sight is rotated through the same angle toward the left and thereafter the mortar barrel is pivoted toward the right until the center of the cross hairs of the sight is once more on the aiming post.
In some cases, it is necessary to fire from a defiladed position, (cave, shell-hole, etc) which does not permit aiming marks, for example aiming posts to be placed at sufficient distances to suitably reduce the aiming error in azimuth. In such cases the accuracy of fire is adversly affected.
It is also necessary to fire such weapons at night and in prior practice, aiming posts with light sources have been placed at selected locations downrange of the mortar where the sighting device is referenced on the light sources. Such arrangements have been generally unsatisfactory in that the aiming posts are easily sighted by the enemy and can be used to indicate the position of the mortar.